The use of 2,2,6,6-tetraalkyl-4-piperidylamines, such as N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine, as ultraviolet stabilizers for polymeric materials is well known in the art. In the past, the production of these compounds has generally involved the use of a platinum, nickel or cobalt catalyst in an aliphatic alcohol solvent.
Thus, U.S. Pat. No. 4,104,248 issued to G. Cantatore shows the production of N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)ethylenediamine employing a platinum or carbon catalyst and utilizing methanol as a reaction medium. Similarly, U.S. Pat. No. 4,326,063 issued to P. N. Son discloses a process for producing 2,2,6,6-tetraalkyl-4-piperidylaminocycloalkyl compounds utilizing a platinum catalyst and a polar organic solvent, such as an aliphatic (lower alkyl) alcohol, while Minagawa et al in U.S. Pat. No. 4,415,688 show the production of certain 2,2,6,6-tetraalkylpiperidylamine compounds employing a platinum/carbon catalyst and methanol as the solvent.
Somewhat similarly, in German Offenlegungschrift No. 3,007,996, a Raney nickel or cobalt catalyst is employed in an inert organic solvent to produce polyalkylpiperidylamines.
Although such prior art process will produce 2,2,6,6-tetraalkyl-4-piperidylamines in desirable yields, the pyrophoric nature of the platinum, nickel or cobalt catalysts utilized coupled with the flammable solvents employed present a potential hazard. Thus, P. N. Rylander, Catalytic Hydrogenation Over Platinum Metals, page 12, Academic Press (1967), has stated "Platinum metal catalysts are generally nonpyrophoric and can be safely held in the hand. However, they catalyze the oxidation of organic compounds and great care must be taken when the catalysts are brought into contact with organic liquids or combustible vapors. Platinum metal catalysts, especially platinum or palladium, are prone to ignite lower alcohols." Moreover, the same author has cautioned, in Catalytic Hydrogenation in Organic Syntheses, page 3, Academic Press (1979), that "Virgin catalysts, such as Raney nickel, which contain dissolved hydrogen ignite when exposed to air, and due care should be taken in handling . . . " and, further, that "Metal catalysts on finely divided carbon are subject to dust explosions, just as carbon itself or flour is." Consequently, it would be desirable to possess a process for producing 2,2,6,6-tetraalkyl-4-piperidylamines which process would avoid the potential health hazard associated with such prior art processes.
As is discussed in some detail below, the mechanism of the reaction between amines and 2,2,6,6-tetraalkyl-4-piperidones in the production of 2,2,6,6-tetraalkyl-4-piperidylamines involves an equilibrium reaction between (A) an alkanolamine on one hand and (B) a ketimine and water on the other, with the ketimine subsequently being hydrogenated to form the product 2,2,6,6-tetraalkyl-4-piperidylamine.
Therefore, it is completely unexpected that the use of a reaction medium comprising at least about 10 weight percent water in the platinum, nickel or cobalt catalyzed production of 2,2,6,6-tetraalkyl-4-piperidylamines would not only reduce the threat of flammability presented by such pyrophoric catalysts, but would additionally not materially affect the amount of substituted piperidylamine produced.